Dysphagia refers to any deglutition (swallowing) disorder, including abnormalities within the oral, pharyngeal and esophageal phases of swallowing. Dysphagia is common in individuals with neurological impairment, due to, for example, cerebral palsy, cerebrovascular accident, brain injury, Parkinson's disease, stroke and multiple sclerosis. Individuals with dysphagia are often at risk of aspiration. Aspiration refers to the entry of foreign material into the airway during inspiration. Aspiration may manifest itself in a number of different ways. The individual may begin to perspire and the face may become flushed. Alternatively, the individual may cough subsequent to swallowing. In silent aspiration, there are no overt clinical or easily recognizable signs of bolus inhalation. The invention is particularly useful for individuals with silent aspiration, but is also applicable for other manifestations of aspiration. Aspiration bears serious health consequences such as chronic lung disease, aspiration pneumonia, dehydration, and malnutrition.
Dysphagia afflicts an estimated fifteen million people in the United States. Certain sources indicate that fifty thousand people die each year from aspiration pneumonia (Dray et al., 1998). The occurrence of diffuse aspiration bronchiolitis in patients with dysphagia is not uncommon, regardless of age (Matsuse et al., 1998). Silent aspiration is especially prominent in children with dysphagia, occurring in an estimated 94% of that population (Arvedson et al., 1994). Half of stroke survivors have swallowing difficulties (Zorowitz & Robinson, 1999), which translates to 500,000 people per year in the United States, (Broniatowski et al., 2001), and aspiration is reported in 75% of these cases while 32% report chest infections (Perry & Love, 2001). The incidence of dysphagia is particularly significant in acute care settings (25-45%), chronic care units (50%) (Finiels et al., 2001) and homes for the aged (68%) (Steele et al., 1997). Dysphagia tremendously diminishes quality of life for people of all ages, compromising not only medical, but social, emotional and psychosocial well-being.
The modified barium swallow using videofluoroscopy is the current gold standard for confirmation of aspiration (Wright et al., 1996). Its clinical utility in dysphagia management continues to be asserted (e.g., Martin-Harris, 2000; Scott et al., 1998). The patient ingests barium-coated material and a video sequence of radiographic images is obtained via X-radiation. The modified barium swallow procedure is invasive and costly both in terms of time and labor (approximately 1,000 health care dollars per procedure in Canada), and renders the patient susceptible to the effects of ionizing radiation (Beck & Gayler, 1991).
Fibreoptic endoscopy, another invasive technique in which a flexible endoscope is inserted transnasally into the hypopharynx, has also been applied in the diagnosis of post-operative aspiration (Brehmer & Laubert, 1999) and bedside identification of silent aspiration (Leder et al., 1998). Fibreoptic endoscopy is generally comparable to the modified barium swallow in terms of sensitivity and specificity for aspiration identification (e.g., Madden et al., 2000; Leder & Karas, 2000), with the advantage of bedside assessment. Pulse oximetry has been proposed as a non-invasive adjunct to bedside assessment of aspiration (e.g., Sherman et al., 1999; Lim et al., 2001). However, several controlled studies comparing pulse oximetric data to videofluorscopic (Sellars et al., 1998) and fiberoptic endoscopic evaluation (Leder, 2000; Colodny, 2000) have raised doubts about the existence of a relationship between arterial oxygen saturation and the occurrence of aspiration.
Cervical auscultation involves listening to the breath sounds near the larynx by way of a laryngeal microphone, stethoscope or accelerometer (Zenner et al., 1995) placed on the neck. It is generally recognized as a limited but valuable tool for aspiration detection and dysphagia assessment in long-term care (Zenner et al., 1995; Cichero & Murdoch, 2002; Stroud et al., 2002). However, when considered against the gold standard of videofluoroscopy, bedside evaluation even with cervical auscultation yields limited accuracy (40-60%) in detecting aspirations (Sherman et al., 1999; Selina et al., 2001; Sellars et al., 1998). Indeed, our recent research shows that aspirations identified by clinicians using cervical auscultation, represent only a quarter of all aspirations (Chau, Casas, Berall & Kenny, submitted).
Swallowing accelerometry (Reddy et al., 2000) is closely related to cervical auscultation, but has entailed digital signal processing and artificial intelligence as discrimination tools, rather than trained clinicians. In clinical studies, accelerometry has demonstrated moderate agreement with videofluoroscopy in identifying aspiration risk (Reddy et al., 1994) where as the signal magnitude has been linked to the extent of laryngeal elevation (Reddy et. al, 2000). Recently, fuzzy committee neural networks have demonstrated extremely high accuracy at classifying normal and “dysphagic” swallows (Das et al., 2001). However, prior art swallowing accelerometry only provides limited information in classifying normal from “dysphagic” swallows and does not provide broader information about the clinical status of the patient.
Administration of videofluoroscopy or nasal endoscopy requires expensive equipment and trained professionals such as a radiologist, otolaryngologist or speech-language pathologist (Sonies, 1994). Invasive procedures are not well-tolerated by children and cannot be practically administered for extended periods of feeding. There is a need for an economical, non-invasive and portable method of aspiration detection, for use at the bedside and outside of the institutional setting.